Belly Fat Bad for Men's Bones

Nov. 28, 2012 (Chicago) -- Obese men with beer bellies may be at greater risk of weak bones and fractures than obese men whose fat tends to gather in the thighs and buttocks, a small study suggests.

Previous research has shown that belly fat is bad for women's bones. So when a recent study showed that obese men have more fractures than their non-obese counterparts, Harvard researchers wanted to find out if the type of fat mattered in men, too.

"What we found is that obese men with deep belly fat had much, much weaker bones than other obese men," says researcher Miriam Bredella, MD, a radiologist at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School.

The study doesn't prove cause and effect. Still, "men need to be aware that excess belly fat is a risk factor not only for heart disease and diabetes, but also for bone loss," she says.

The findings were presented here today at the annual meeting of the Radiological Society of North America.

Obesity: Bad for the Bones

According to the National Center for Health Statistics, more than 37 million American men over age 20 are obese. Obesity is associated with many health problems, including heart disease, stroke, and diabetes.

But for years, obesity and body fat were thought to have at least one redeeming quality: Stronger bones and a lower risk for osteoporosis and related fractures, says Thomas Link, MD, professor of radiology at the University of California, San Francisco.

That belief was crushed by a study linking obesity to fractures as well as two other studies linking body fat to weaker bones and lower bone density, he says.

The new study puts the nail in the coffin and takes the research a step further, Link says.

"It shows that obese patients with a lot of fat around the gut and liver have less bone strength and lower bone quality, and are probably at great risk of osteoporosis and osteoporotic fractures," he says. He was not involved with the study.

Belly Fat Bad for the Bones: Study Details

Bredella and colleagues studied 35 obese but otherwise healthy men whose average age was 34.

Their average body mass index, or BMI, was 36.5; values of 30 and higher are considered obese.

The men underwent CT scans of the abdomen and thigh to assess fat and muscle mass. Then they were divided into two groups, depending on whether they had more visceral (belly) fat located deep under the muscle tissue in the abdomen or more fat located below the skin in the thigh and buttock areas.

Then the researchers took high-resolution CT scans of the men's forearms and wrists. A sophisticated computer technique was used to assess bone strength and predict fracture risk.

"It's a technique that is frequently used in mechanical engineering to determine the breaking point of materials used in the design of bridges and airplanes, among other things," Bredella says.

Because use of the technique to measure bone strength is so novel, researchers don't know for sure what normal values should be. "But what we can say is that the more belly fat a man had, the weaker his bones," she says.

Overall, the researchers predicted that obese men with deep belly fat would be 25% more likely to break a bone than obese men with more superficial fat.

They also found an association between greater muscle mass and increased bone strength; however BMI and age had no effect on bone strength.

What to Do?

So what's an obese man with a lot of belly fat to do?

Where you gain fat is for the most part genetically determined, Bredella says. "But it is one more reason not to gain excess weight in the first place," she says.

Weight-bearing exercises like brisk walking and aerobics are "really good for building strong bone," she says. And resistance and strength training exercises such as lifting weights and climbing stairs are also helpful, Bredella says.

These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.